Electrically insulating sealing structure and its method of use in a semiconductor manufacturing apparatus

ABSTRACT

In accordance with the present invention, an insulating sealing structure useful in physical vapor deposition apparatus is provided. The insulating sealing structure is capable of functioning under high vacuum and high temperature conditions. The apparatus is a three dimensional structure having a specifically defined range of electrical, chemical, mechanical and thermal properties enabling the structure to function adequately as an insulator which does not break down at voltages ranging between about 1,500 V and about 3,000 V, which provides a seal against a vacuum of at least about 10 −6  Torr, and which can function at a continuous operating temperature of about 300° F. (148.9° C.) or greater. The insulating sealing structure may be fabricated solely from particular polymeric materials or may comprise a center reinforcing member having at least one layer applied to its exterior surface, where the at least one surface layer provides at least a portion of the insulating properties and provides the surface finish necessary to make an adequate seal with a mating surface.

This application is a divisional application of application Ser. No.08/899,685 of Demaray et al., Filed Jul. 24, 1997 now U.S. Pat. No.6,033,483, which is a continuation-in-part of U.S. application Ser. No.08/268,480, filed Jun. 30, 1994 now abandoned.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This patent application is a continuation-in-part of U.S. patentapplication Ser. No. 08/268,480, filed Jun. 30, 1994, and entitled “AnElectrically Insulating Sealing Structure And Its Method Of Use In AHigh Vacuum Physical Vapor Deposition Apparatus”.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to an electrically insulating sealingstructure which can be used in semiconductor processing such as physicalvapor deposition (sputtering). The electrically insulating sealingstructure is particularly useful in processing apparatus requiringoperation at a vacuum of at least 10⁻⁶ Torr and continuous use attemperatures ranging from about −10° F. (−23.2° C.) to about 750° F.(400° C.).

2. Description of the Background Art

Sputtering describes a number of physical techniques (such as DC plasmaenhanced sputtering, RF plasma, and ion gun) commonly used in thesemiconductor industry for the deposition of thin films of variousmetals such as aluminum, aluminum alloys, refractory metal silicides,gold, copper, titanium-tungsten, tungsten, molybdenum, tantalum and,less commonly, silicon dioxide and silicon onto an item (a substrate).In general, the techniques involve producing a gas plasma of ionizedinert gas “particles” (atoms or molecules) by using an electrical fieldin an evacuated chamber. The ionized particles are then directed towarda “target” and collide with it. As a result of the collisions, freeatoms or groups of ionized atoms of the target material are ejected fromthe surface of the target, essentially converting the target material tothe free atoms or molecules. The free atoms escaping the target surfaceare directed toward the substrate and form (deposit) a thin film on thesurface of the substrate.

A typical plasma sputtering process uses a magnetic field to concentratethe plasma ions performing the sputtering action in the region of themagnetic field so that target sputtering occurs at a higher rate and ata lower process pressure. In DC sputtering, the target itself iselectrically biased with respect to the substrate on which the sputteredmaterial is to be deposited and with respect to the sputter processingchamber. The sputtering target functions as a cathode, with thesubstrate (depending on the composition of the substrate), the platformon which the substrate sits, and/or the process chamber functioning asan anode. A high voltage, typically between about 200 and 800 volts, isapplied between these two electrodes, with the substrate disposed upon aplatform positioned opposite the cathode. The pressure in the sputterprocessing chamber is typically reduced to about 10⁻⁶ to 10⁻⁹ Torr,after which argon, for example, is introduced to produce an argonpartial pressure ranging between about 10⁻² to about 10⁻⁴ Torr.Considerable energy is used in generating the gas plasma and creatingion streams impacting on the cathode, and it is not unusual for thetemperature of the internal walls, in particular the dark space shieldinside the sputter processing chamber, to rise above 750° F. (400° C.).

Recent developments in liquid crystal flat panel display technology haveresulted in an interest in processing apparatus capable of carrying outsputtering on a particularly large scale. For example, rectangular flatpanels approximately 15 in. by 19 in. (0.38 m×0.48 m) are not uncommon,with the industry moving toward 48 in. by 48 in. (1.2 m×1.2 m) panels.To achieve acceptable display performance over such a large surfacearea, it is necessary that the conductivity of the metallized electrodesin the underlying semiconductor device, which controls operation of theliquid crystal composition, be especially high. To achieve this highconductivity, technologists would like to use aluminum for themetallized electrodes; however, aluminum oxides form very rapidly in thepresence of oxygen, contaminating the deposited aluminum layer andreducing its conductivity. To be able to sputter deposit a low stressfilm of pure layer of aluminum having the desired conductivity, it isnecessary to carry out the sputtering operation at a particularly highvacuum. This reduces the partial pressure of residual ambient aircomponents such as oxygen and water vapor which lead to oxidation of thedepositing aluminum. For example, in a sputtering process chamberevacuated to 10⁻⁶ Torr, residual oxygen in the sputtering chamber willdeposit a monolayer of oxygen upon an aluminum substrate surface withinapproximately one second; however, at 10⁻⁹ Torr, it takes about 1,000seconds to deposit a monolayer of oxygen upon the substrate. This makesit desirable to deposit the conductive aluminum layer in processchambers for which the base pressure is less than 10⁻⁶ Torr, andpreferably at 10⁻⁸ to 10⁻⁹ Torr, to obtain a satisfactory conductivityof a low-stress deposited aluminum layer.

FIG. 1 shows an exploded view of a sputtering process apparatus 100 ofthe kind used to produce flat panel display semiconductor devices. Thesputtering process chamber 138 is accessed through a slit-valve opening145 such that a substrate to be deposited upon (not shown) is deliveredto a sputtering pedestal 146. The insulating structure used to insulatetarget assembly 124 (the cathode) from process chamber 138 (the anode)includes an outer insulator 134 and a main insulator 133. Targetassembly 124 is further insulated from chamber cap 113 using upperinsulator 117. Power is applied via power connection 155 whichprogresses through the apparatus through power connection hole 92.Vacuum passage 156 provides evacuation capability for the chamber cap113, and a cooling manifold (not shown) included as a part of targetassembly 124, provides cooling for the sputtering target. A moredetailed description of this sputtering process chamber and itsfunctioning is available in patent application Ser. No. 08/236,715 ofRichard E. Demaray et al., filed Apr. 29, 1994 now U.S. Pat. No.5,487,822, and commonly owned by the assignee of this application, whichcopending patent application is hereby incorporated by reference in itsentirety.

Typically upper insulator 117 and outer insulator 134 are constructedfrom a plastic material such as, for example, acrylic or polycarbonate,as these insulators are not exposed to the high temperatures experiencedby main insulator 133 and are subjected to less severe vacuum sealingrequirements than main insulator 133. In the past, the main insulator133 has been constructed from a ceramic material, for example 99.7% purealuminum oxide (alumina) or quartz, to provide the dielectric propertiesrequired at operating conditions. Typical operating conditions exposethe ceramic material to voltages as high as 1,000 volts, at temperatureswhich may be as high as about 750° F. (400° C.) and which are frequentlyas high as about 400° F. (204.4° C.). Further, main insulator 133 mustalso be able to sustain high compressive loads (several tons) and tomake a vacuum seal with a process chamber base pressure preferably inthe range of 10⁻⁸ to 10⁻⁹ Torr. Thus, the material of construction ofthe main insulator must meet stringent requirements.

FIG. 2A shows a cross sectional view of an assembled sputtering processchamber of the kind shown in FIG. 1. Particular detail definition in thearea of main insulator 133 is shown in FIG. 2B. The target assembly 124has a target backing plate 128 and O-ring groove 129 which is fittedwith an elastomeric O-ring (not shown), typically Viton® (fluorocarbon,trademark of Du Pont Co., Wilmington, Del.), which seals against bothtarget backing plate 128 and ceramic main insulator 133. Ceramic maininsulator 133 is further sealed against sputtering chamber 138 via anO-ring groove 139 in the top flange of sputtering chamber 138, whichalso contains an elastomeric O-ring (not shown) constructed from amaterial such as Viton®. FIG. 2B shows the directional indicator P,indicating the direction perpendicular to seal which will be referred tosubsequently herein.

Main insulator 133 is particularly difficult to fabricate and to handledue to the mechanical properties of the alumina from which it isfabricated. Main insulators which are 48 in. by 48 in. (1.2 m×1.2 m) inexterior dimension, having a width of approximately 1 in. (0.0254 m) anda thickness of about 0.5 in. (0.0127 m) are particularly difficult andcostly to fabricate, and are difficult to handle without damage duringsputter processing operations. Further, due to the notch sensitivity ofcrystalline ceramic materials, it is not practical to machine a grooveinto the surface of main insulator 133. Thus, the groove 129 used toprovide support for the O-ring means of sealing between sputter targetassembly 124 and main insulator 133 must be machined into the surface oftarget assembly 124. Since target assembly 124 is consumed duringoperation of the sputtering apparatus, the groove must be machined intoeach new, consumable sputtering target, adding to the cost of thetarget.

It would be highly desirable to have a main insulator having thenecessary dielectric properties and having adequate mechanicalproperties to function in the application while providing ease infabrication and handling.

SUMMARY OF THE INVENTION

In accordance with the present invention, an apparatus useful insemiconductor processing is provided; the apparatus functions as anelectrical insulator and provides a sealing surface for use insemiconductor processing operations carried out under high vacuum andhigh temperature. In particular, the apparatus is a three dimensionalstructure fabricated using material having a specifically defined rangeof electrical, chemical, mechanical and thermal properties. The threedimensional structure may be formed from a single material or from acomposite of materials. Preferably the three dimensional structure has arigid or rigidized center portion or member and an exterior surfacewhich can be deposited, cured or polished to have a surface roughnessheight value of about 16μ in. (0.40 μm) or less in the directionperpendicular to seal. Typically the rigid member will be formed from adifferent material that used to provide the exterior surface. Thestructure may be of single piece construction, molded, machined, or castdirectly to the desired dimensions, may be a rigid center member with aninorganic or an organic coating (or a combination thereof) applied toits exterior surface, or may be an assembly of multiple pieces joinedtogether using various techniques.

The apparatus comprising the insulating structure should not decomposeunder vacuum, and any outgassing of water or absorbed gases must besufficiently small to sustain a base pressure of at least 10⁻⁶ Torr, andpreferably 10⁻⁸ to 10⁻⁹ Torr. The sealing surface of the insulatingsealing structure should be capable of being polished to a roughnessheight value of about 16 μin (0.40 μm) or less in the directionperpendicular to seal. The insulating, sealing structure should alsoexhibit a dielectric strength in air of at least 50 KV/in (1.96 MV/m)and a deflection temperature @ 264 PSI (1.82 MPa) of at least 300° F.(148.9° C.).

When the insulating sealing structure is constructed from pieces whichare joined together, this joining may be by mechanical fastening means,by physical means such as diffusion bonding or solvent bonding, bychemical means such as covalent or ionic bonding using an adhesive, orby other appropriate method. However, a one piece structure ispreferable, due to the high vacuum conditions under which the sealingperformance must occur.

One preferred embodiment of the insulating sealing structure comprises agroove machined on at least one surface of the structure which enablesthe structure to be used in combination with an elastomeric O-ring, toachieve an adequate seal at minimal contact pressures between theinsulating sealing structure and any other surface with which a seal isto be formed.

A second preferred embodiment of the insulating sealing structurecomprises a continuous contacting bead or molding which has beenmachined upon or formed on at least one surface of the structure. Thecontinuous contacting bead or molding eliminates the need for an O-ringto provide a seal with a mating surface. This continuous bead or moldingcan be in the shape of a triangle, rising to a relatively narrow uppersurface which forms the line of continuous contact which makes the seal.The continuous bead or molding can be in a more rounded, mound shape, oranother appropriate design which optimizes the ability of the continuousbead to provide an adequate seal with a mating surface.

A third preferred embodiment of the insulating sealing structurecomprises the insulating sealing structure having on at least one of itssurfaces a continuous coating of an insulating and/or elastomericmaterial which assists the insulating sealing structure in making anadequate seal with a mating surface.

In a fourth preferred embodiment, the insulating sealing structurecomprises a center reinforcing member having at least one layer appliedto its exterior surface, where the at least one surface layer providesat least a portion of the insulating properties of the insulatingsealing structure and provides the surface finish necessary to make anadequate seal with a mating surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exploded view of a sputtering process chamber of thekind used to produce flat panel display semiconductor devices.

FIG. 2A shows a cross-sectional view of an assembled sputtering processchamber of the kind shown in FIG. 1, with particular definition in thearea of the main insulator, upper insulator, and lower insulator.

FIG. 2B shows a cross sectional detail view of the area of the maininsulator, upper insulator , and lower insulator defined in FIG. 2A.

FIG. 3A illustrates a top view of a rectangular-shaped main insulator ofthe kind typically used in sputtering apparatus for flat panel displays.In particular, the rectangular shaped structure is formed from fourpieces of sheet stock which are joined together using a flush lap jointat each of the four corners of the rectangle.

FIG. 3B shows the side view of one of the four members used to fabricatethe rectangular-shaped main insulator of FIG. 3A.

FIG. 4A shows a side view of a flush lap joint of the main insulatorillustrated in FIG. 3A. In particular, the flush lap joint has beenmodified using a triangular-shaped insert to stop leakage which occurredat the lap joint upon exposure to sputtering operational conditions.

FIG. 4B shows a top view of the modified lap joint of FIG. 4A. Excessinsert material is removed to provide a flush top surface.

FIG. 5 shows a main insulator for use in a sputtering process chamber ofthe kind shown in FIG. 1. This main insulator has an O-ring groovemachined into its sealing surface.

FIG. 6A shows a cross sectional view of an O-ring groove of the kinddepicted in FIG. 5, which is machined into the sealing surface of a maininsulator of the present invention.

FIG. 6B shows a cross sectional view of a second O-ring groove of thekind depicted in FIG. 5, with an O-ring, preferably elastomeric, inplace.

FIG. 6C shows a cross sectional view of an alternative groove structurewhich could be machined along the edge of a main insulator and fittedwith a capping structure, preferably elastomeric, which provides asealing surface for the main insulator.

FIG. 7A shows a cross sectional view of a sealing bead machined upon thesealing surfaces of a main insulator of the present invention.

FIG. 7B shows a cross sectional view of an alternative sealing beadmachined upon the sealing surfaces of a main insulator of the presentinvention.

FIG. 7C shows a cross sectional view of a layer of sealing material,preferably a dielectric and/or elastomeric material, deposited upon thesealing surfaces of a main insulator of the present invention.

FIG. 7D shows a cross sectional view of an enclosing sealing material,preferably a dielectric and/or elastomeric material, deposited upon themajor surfaces of a main insulator of the present invention.

FIG. 8A shows a cutaway perspective view of an embodiment of the maininsulator of the present invention having a rigid composite centermember with an exterior surface sealing layer or coating.

FIG. 8B shows a cutaway perspective view of an embodiment of the maininsulator of the present invention having a rigid center member whichhas been treated to create an overlying first layer which providesparticular insulating and bonding characteristics, followed byapplication of a second layer which provides the desired sealingsurface.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to an electrically insulating structuralcomponent of a semiconductor processing apparatus. The structuralcomponent is three dimensional, and is typically used as the maininsulator in a sputtering process apparatus, insulating the cathodeportion of the apparatus from the anode portion of the apparatus.

The insulating structure (insulating apparatus) is typically used inhigh vacuum systems where the base pressure vacuum exceeds 10⁻⁶ Torr.Due to the degree of vacuum involved, sealing of the sputtering processapparatus from ambient atmosphere is a significant problem. Theinsulating structure must perform adequately as a sealing structure aswell as an insulating structure when used in the manner illustrated inFIG. 1.

The important electrical, chemical, mechanical, thermal and surfaceproperties which should be provided by the combination of the materialsof construction and the structure into which they have been fabricatedare as follows:

1) The apparatus comprising the insulating sealing structure should notdecompose under vacuum and any outgassing of water, other volatiles, andabsorbed gases must be sufficiently small to sustain a base pressure ofat least 10⁻⁶ Torr, and preferably 10⁻⁸ to 10⁻⁹ Torr. This means atleast the exterior surface material of the insulating sealing structureshould not decompose under vacuum and all materials which make up thestructure should not contain elements or compounds which will outgas inamounts which cause problems under operational conditions to which theinsulating sealing structure will be exposed. For example, the materialsmust not contain water or oxygen, for example, in excessive amounts asoriginally fabricated, and must resist the absorption of water duringstorage and use, for example. In the present instance, water absorptionfor a polymeric material, determined using ASTM D-570 should not exceedabout 0.25% in 24 hrs @ 73° F. (22.8° C.). ASTM D-570 is one of manytesting standards promulgated by the American Society for Testing andMaterials of Philadelphia, Pa.

2) The sealing surface of the insulating sealing structure should becapable of being polished to a roughness height value of about 16 μin(0.40 μm), preferably 8 μin (0.20 μm) in the direction perpendicular tothe seal. The ability of a polymeric material or an inorganic materialto be polished to a roughness height value in the range of 0.40 μm orlower is of particular importance, as it affects the ability to obtain aseal adequate to enable establishment of a vacuum of at least 10⁻⁶ Torr.

3) The insulating sealing structure should show adequate maintenance ofdielectric properties and of dimensional and mechanical stability, tocontinue to function adequately at continuous exposure to at least about10⁻⁶ Torr and at a continuous operating temperature of about 300° F.(148.9° C.) or greater, for a time period adequate to meet productionneeds, preferably for at least several weeks. The dielectric propertiesand dimensional and mechanical properties known to provide an adequateinsulating sealing structure are those listed below, as an insulatingsealing structure having such properties has performed satisfactorilyunder continuous operating conditions of about 10⁻⁶ Torr and at 300° F.(148.9° C.) or greater.

a) Dielectric strength in air (of a {fraction (1/16)} in. (1.7 mm) thicksample) of at least 50 KV/in. (1.96 MV/m), as measured using ASTM D-149;or volume resistivity at 73° F. (22.8° C.) of at least 10¹⁰ Ω-m, asmeasured using ASTM D-257.

b) a linear coefficient of expansion of less than about 50×10⁻⁶ in/in/°F. (90 ×10⁻⁶ mm/mm/° C.), as measured using ASTM E-228.

c) a deflection temperature @ 264 PSI (1.82 MPa) of at least 300° F.(148.9° C.).

d) an ultimate compressive strength greater than about 15,000 PSI (103.4MPa), as measured using ASTM D-695.

When the insulating sealing structure is constructed from pieces whichare joined together, this joining may be by mechanical fastening means,by physical means such as diffusion bonding or solvent bonding, bychemical means such as covalent or ionic bonding using an adhesive, orby other appropriate method. However, a one piece structure ispreferable, due to the high vacuum conditions under which the sealingperformance must occur.

FIG. 1 shows an exploded view of a sputtering process apparatus 100, ofthe kind used to produce flat panel display semiconductor devices. Thesputtering process apparatus 100 includes a main insulator 133 whichprovides electrical insulation between target assembly 124 (which actsas a cathode) and sputtering process chamber 138 (which acts as ananode). The voltage across main insulator 133 typically ranges fromabout 200 to about 800 volts. The amount of vacuum present at thelocation of main insulator 133 is minimally 10⁻⁶ Torr, and preferablyranges between about 10⁻⁸ and 10⁻⁹ Torr. In addition, the continuousoperational temperature present at the location of main insulator 133 isminimally about 100° F. (37.8° C.) and may rise as high as about 550° F.(287.8° C.). The compressive pressure exerted on the surface of maininsulator 133 is typically about 75 lb./lineal inch, (13.1 N/lineal mm),but can rise to at least 2 to 3 times that amount, depending on the sizeof the sputtering process apparatus and process conditions utilized.

Main insulator 133 has been constructed from alumina and quartz in thepast. The preferred alumina is 99.5% minimum purity and has a density ofabout 2.2 to 2.4 g./cc. This material of construction provides an outgasrate of less than about 2.0×10⁻⁷ Torr—liter/sec/cm² under sputteringprocess conditions. The water absorption of fired alumina of the kindused to fabricate insulators has been observed to be particularly lowupon exposure to ambient atmosphere, so this is not a factor. Thesurface of the main insulator structure constructed from alumina can bepolished to a roughness height value of 8 μin (0.20 μm) in the directionperpendicular to seal. The dielectric strength for the alumina materialin air is about 250 kV/in. (9.8 MV/m). The volume resistivity of thealumina material is at typically 10¹² to 10¹⁴ Ω-cm. The linearcoefficient of expansion for the alumina material is 9×10⁻⁶ in./in./° F.(16.2 mm/mm/° C.). The ultimate compressive strength for the aluminamaterial can range from about 15,000 to about 60,000 PSI (103-414 MPa).One skilled in the art can see that the alumina material can meet theelectrical and vacuum performance criteria previously specified for anelectrical insulating material to be used for main insulator 133.

However, as the technology in flat panel display has developed sosuccessfully, as previously described, there has been an increasingdesire to produce larger display panels, leading to the desire forlarger dimensional sputtering capability. As dimensions of sputteringchamber 138 (FIG. 1) have increased, the perimeter dimensions of maininsulator 133 have increased in proportion. As a result, it is presentlydesired to have a rectangular-shaped main insulator 133 about one inch(0.0254 m) in width and about one half inch (0.0127 m) in thickness andhaving a length of about 48 inches (1.2 m) on each of its four sides.Construction of a main insulator of these dimensions would require useof a sheet of “green” alumina approximately 48 inches (1.2 m) square andone half inch (13 mm) thick, which would enable machining of acontinuous (jointless) structure. Alternatively, the structure wouldhave to be cast directly to dimension by the alumina manufacturer. Thejointless structure is required due to the inability to join pieces ofalumina together in a manner which will not leak across the joint uponapplication of a vacuum of at least 10⁻⁶ Torr across the joint whilemaintaining electrical insulation. Either of these methods ofconstruction of an alumina main insulator 133 are extremely expensive.In fact, the cost of a main insulator fabricated to these dimensionswould be about 2.5 to 3 times higher than the same insulator fabricatedfrom the polymeric materials of the present invention.

In addition, the alumina is a very brittle, crystalline material,increasing the possibility of damage to main insulator 133 upon handlingduring sputtering process operations. For example, the Tensile Strengthfor alumina ranges from about 700 to about 3,000 PSI (4.8-20.7 MPa) andImpact Strength (unnotched) ranges from about 0.17 to about 0.25 ft-lb(0.34 J); ½ in. (13 mm) rod. This compares with Tensile Strength for thepolymeric materials of the present invention ranging from about 5,000 toabout 15,200 PSI (34-105 MPa), and an unnotched Izod Impact Strengthranging from about 25 to about 30 ft-lb/in. (1,300-1,600 J/m).

It is highly desirable to use an insulating material which has thenecessary dielectric properties and adequate mechanical properties tofunction in the application, while providing ease in fabrication andhandling. For this reason, outer insulator 134 and upper insulator 117of sputtering process apparatus 100 illustrated in FIG. 1 are typicallyconstructed from a plastic material such as, for example, acrylic orpolycarbonate. However, these materials cannot be used for fabricationof main insulator because of creep and poor compressive strength atelevated temperature and poor high vacuum performance.

High temperature, high performance engineering plastics such as Vespel®polyimide (available from DuPont); Arlon®, polyetheretherketone(available from Greene, Tweed & Co.); and, Ultem® polyetherimide(available from General Electric) have been used in high temperaturesemiconductor applications for construction of a number of smallstructures such as bearing surface coatings, bushings, washers andspacers. However, these materials have not been used to construct a partlike the main insulator of the present invention, because of the largesize sheet required, and possibly because of the numerous foreseeableproblems in such an application.

The more significant barriers to use of these kinds of materials infabrication of main insulator 133 relate to outgassing characteristicsof the materials under process operational conditions, and to theability to seal against the 10⁻⁸ to 10⁻⁹ Torr operational vacuum,particularly at continuous operational temperatures in the range of 400°F. (204.4° C.) to 550° F. (287.8° C.).

The Table, below, shows particularly important physical and mechanicalproperties for Ultem® 1000 polyetherimide, Vespel® SP-1 polyimide,Arlon® 1000 polyetheretherketone. These high temperature, highperformance engineering plastics, and others demonstrating equivalentperformance properties to those shown in the Table, can be used as thesole material of construction for the insulating sealing apparatus ofthe present invention or as a surface layer applied over an interiorrigidizing structure.

Other additional high performance engineering plastics useful infabrication of the insulating sealing apparatus include: G-3 gradefiberglass-reinforced phenolic which meets the military specificationMil-I-24768/18-GPG; G-10 and G-11 grade fiberglass-reinforced epoxieswhich meet the military specifications Mil-I-24768/2/27-GEE, GEE-F andMil-I-24768/3-GEE, respectively. These materials have previously beenused as an ablative material in aerospace applications. Theseengineering plastics or an equivalent epoxy or phenolic-based material,the surface of which has been polished to a surface roughness of about16 μin (40 μm) or less can be used.

TABLE Linear Dielectric Volume Coefficient of Strength ResistivityExpansion kV/in. Ω-cm in./in./° F. Material ASTM D-149 ASTM D-257 ASTMD-696 ULTEM ® 1000 830 6.7 × 10¹⁷ 31 × 10⁻⁶ VESPEL ® SP-1 560 10¹⁶-10¹⁷30 × 10⁻⁶ ARLON ® 1000 480 4-9 × 10¹⁶ 26 × 10⁻⁶ ≦ 302° F. 60 × 10⁻⁶ ≧302° F. Notched Water Tensile Izod Impact Absorption Elongation Strength% % ft-lbs./in. Material ASTM D-570 ASTM D-1708 ASTM D-256 ULTEM ® 10000.25 60 1.0 VESPEL ® SP-1 0.24 7.5-8.0 1.5 ARLON ® 1000 0.14 35 1.6Deflection Ultimate Temperature Compressive ° F. @ 264 PSI StrengthMaterial ASTM D-648 ASTM D-695 ULTEM ® 1000 392 21,900 VESPEL ® SP-1 68019,300 ARLON ® 1000 360 17,110

EXAMPLE

A rectangular main insulator was fabricated using ULTEM® 1000 to thedimensions described below, with reference to FIGS. 3A and 3B, whichshow the top view of the main insulator and a side view of one member,respectively. Two members, 310 and 312 of rectangular main insulator 133were fabricated to a dimension A of 26.7 inches (0.678 m) in length. Theremaining two members 314 and 316 were fabricated to a dimension B of23.2 inches (0.589 m) in length. The four members 310, 312, 314, and 316were fastened together using a flush lap joint 317 at each end of eachmember. The flush lap joints 317 are illustrated in FIG. 3A. Lap joint317 has a dimension C of 1.5 inches (38 mm) and is symmetrical so thatthis dimension applies to the length of the joint in the principaldirection of each member it joins. The external radius 318 of lap joint317 is approximately 0.75 inches (19 mm), while the internal radius 319is about 0.50 inches (13 mm). The flush lap joints were prepared usingstandard solvent bonding techniques. Methylene chloride was used toswell (partially solvate) each surface to be bonded, such as surface 320of member 310, illustrated in FIG. 3B. The surfaces to be bonded werethen pressed together at a pressure of at least 20 PSI (0.138 MPa),exposed to ambient atmosphere, permitting the methylene chloride toevaporate. The width D of main insulator members 310, 312, 314, and 316was 1.0 inches (25.4 mm), and the thickness E was 0.5 inches (13 mm).

Upon completion of assembly of the four members of main insulator 133,the upper and lower surfaces, shown in FIG. 3B as 321 and 322,respectively, were polished to a finish of 8 μin. (0.20 μm) in thedirection perpendicular to seal. The 8 μin. (0.20 μm) finish provided asealing surface for mating with the O-rings (not shown, but located inO-ring grooves 129 and 139) used to create a seal between targetassembly backing plate 128 and main insulator 133, and between the topflange of sputtering chamber 138 and main insulator 133, as illustratedin FIG. 2.

The main insulator 133, fabricated from ULTEM® 1000, was then evaluatedin a sputtering apparatus of the kind shown in FIG. 1. The operationalvoltage applied to main insulator 133 was about 1.0 kV/in. (0.039 MV/m);the vacuum across sealing surfaces of the insulator was 6.7×10⁻⁷ Torr;the maximum temperature of the insulator during evaluation wasapproximately 300° F. (148.9° C.). Pressure leaks were detected at someof the flush lap joints.

Leaks at the flush lap joints were repaired by modifying the lap jointsto include a wedge of ULTEM® 1000 overlaying a portion of the jointnearest the sealing surface, as illustrated in FIGS. 4A and 4B. FIG. 4Ashows a side view of flush lap joint 317 having a wedge 412 of ULTEM1000® solvent-bonded/pressed into place. Wedge 412 overage 414 issubsequently machined to provide a flush surface 321 as shown in theFIG. 4B top view. The solvent bonding of wedge 412 was carried out inthe same manner as previously described for solvent bonding of the flushlap joints. The flush upper surface 321 of each modified joint 317 wasrepolished to the 8 μin.(0.20 μm) finish.

Upon reexposure of main insulator 133 to the evaluation conditionsdescribed above, satisfactory performance was achieved.

It was observed that there was some outgassing from the ULTEM® 1000.This outgassing should be reduced to provide optimum performance of theinsulating sealing structure.

ARLON® 1000 and VESPEL® SP-1 are presently under investigation forperformance characteristics. Should these materials provide improvedoutgassing performance, preparation of a main insulator from sheet stockof these materials will require a different means of joint bonding,since these materials are not known to bond well using solvent bonding.There are a number of adhesives recommended by the manufacturer of eachmaterial and these adhesives are under present evaluation. The preferredadhesive appears to be an epoxy-resin-based, glass-filled adhesiveavailable from American Cyanamid Co. under the trademark of CYBOND 4537Bor CYBOND 4537BHT (a higher T_(g) cured product).

Other, more complex types of joints may provide better vacuum seals, butto date the lap joint has performed as well or better than other jointdesigns evaluated.

It would be preferable to form the insulating sealing structure as asingle, continuous piece having no joints. This can be done by dryingthe polymeric material in pellet or powdered form to remove potentialoutgassing contaminants, followed by melt compression or injectionmolding into the desired insulating sealing structure.

One preferred embodiment of the insulating sealing structure comprises agroove machined on at least one surface of the structure which enablesthe structure to be used in combination with an elastomeric O-ring, toachieve an adequate seal at minimal contact pressures between theinsulating sealing structure and any other surface with which a seal isto be formed. FIG. 5 illustrates main insulator 133 having an uppersealing surface 512 with O-ring groove 510 machined therein. FIG. 6Ashows a cross sectional view of an O-ring groove 610 of the kinddepicted in FIG. 5, which groove 610 is machined into upper sealingsurface 512 and lower sealing surface 612 of main insulator 133. FIG. 6Bshows a cross sectional view of an alternative O-ring groove 614 of thekind depicted in FIG. 5, which O-ring groove 614 is machined into uppersealing surface 512 and lover sealing surface 612 of main insulator 133.An elastomeric O-ring 616 of a high temperature material such as Viton®,for example, is shown in position in O-ring groove 614. FIG. 6C shows across sectional view of an alternative groove structure 622 which couldbe machined along the exterior edge 511 of a main insulator 133.Alternative groove structure 622 is fitted with a capping structure 624preferably comprised of a high temperature elastomeric material able tofunction at 300° F. (148.9° C.) or higher, which provides a sealingsurface for main insulator 133.

A second preferred embodiment of the insulating sealing structurecomprises a continuous contacting bead or molding which has beenmachined upon or formed on at least one surface of the structure. FIG.7A shows a cross sectional view of a sealing bead or molding 710machined upon upper sealing surface 711 and lower sealing surface 713 ofmain insulator 133. FIG. 7B shows a cross sectional view of analternative form of sealing bead 712 machined upon upper sealing surface711 and lower sealing surface 713 of main insulator 133. The continuouscontacting bead or molding eliminates the need for an O-ring to providea seal with a mating surface.

A third preferred embodiment of the insulating sealing structurecomprises the insulating sealing structure having on at least one of itssurfaces a continuous coating of an elastomeric material which assiststhe insulating sealing structure in making an adequate seal with amating surface. FIG. 7C shows a cross sectional view of a layer 714 ofsealing material, preferably a high temperature elastomeric materialsuch as Viton®, for example deposited upon upper sealing surface 711 andlower sealing surface 713 of main insulator 133. FIG. 7D shows a crosssectional view of a bead of sealing material 716, preferably a hightemperature elastomeric material, deposited upon upper sealing surface711 and lower sealing surface 713 of main insulator 133.

In a fourth preferred embodiment, Shown in FIG. 8A, the main insulatorsealing structure 133 has a rigid central portion or member 802 with anelectrically insulating exterior surface layer 804 applied over rigidcentral portion 802. The surface 806 of insulator sealing structure 133is polished to a desired roughness height of less than about 0.40 μm, toenable sealing against a mating surface, where the seal must withstand avacuum of at least 10−6 Torr. Preferably, the surface 806 is polished toa roughness height of less than about 0.20 μm to enable a seal against avacuum of between about 10⁻⁸ and 10⁻⁹ Torr. Surface roughness is acritical factor necessary to enable sealing under extreme vacuumconditions. Not all materials are capable of being cast or polished tomeet this requirement while having the desired dielectric properties andoperational temperature range needed to function in the intendedapplication as previously described.

The rigid central portion 802 is fabricated from materials such asmetal; graphite, glass or polymeric fiber reinforced polymericmaterials; and, polymeric materials having particular structuralcharacteristics. In one preferred embodiment, the metal is aluminum. Inanother preferred embodiment, the rigid central portion 802 is agraphite fiber or glass fiber reinforced polymeric material. In eachcase, the material of construction of rigid central portion 802 must notoutgas in a manner which is detrimental to performance of the insulatingsealing structure and must be thermally and dimensionally stable underoperational conditions previously described for the insulating sealingstructure 133. The rigid central portion 802 inhibits deformation of thestructure 133. Inhibition of deformation is important both in terms ofhandling of the structure and to ensure that the sealing capability ofthe structure is not impaired under extreme vacuum conditions andpressure applied by mating surfaces.

Electrically insulating exterior surface layer 804 provides at least aportion of the required dielectric capability necessary to preventvoltage breakdown under the operating conditions (typically in the rangeof about 1,500 V to about 3,000 V). The required dielectric strength ofsurface layer 804 is at least 1.96 MV/m in air. Exterior surface layer804 is comprised of an insulating material selected from the groupconsisting of phenolic, polyetherimide, polyimide, polyketone,polyetherketone, polyetheretherketone, epoxy, aluminum oxide, siliconoxide, aluminum nitride, silicon nitride, and combinations thereof. Theoverall thickness of surface layer 804 varies according to theelectrical resistivity and dielectric strength of the insulativematerial used to form the insulator. Preferably the insulative materialhas a volume resistivity of at least 10¹² Ω-cm, and more preferably avolume resistivity of at least 10¹⁴ Ω-cm, and a dielectric constant ofat least about 2. When the insulative material has a dielectric constantof about 3.5, surface layer 804 typically ranges from about 10 μm toabout 500 μm in thickness, and more typically from about 100 μm to about300 μm in thickness.

When a polyimide is used as the surface layer 804, the polyimide has adielectric breakdown strength of at least about 100 V/mil (3.9 V/μm).Polyimides which are known to perform in the application include Vespel®SP-1, previously described herein, and UPILEX®, particularly UPILEX® S,manufactured by Uben Industries Ltd., Japan. Optionally, an uncured orpartially cured polyimide 808 may be used as an adhesive to bond asurface layer 804 which is a precured or partially precured polyimidefilm to rigid central portion 802.

Epoxy and phenolic materials are also exhibit an acceptable dielectricbreakdown strength, are capable of performing at temperatures in excessof about 200° C. and can be cast or cast and polished to provide asurface finish having the smoothness necessary to provide the requiredseal. For example, fiberglass-reinforced epoxies of the kind used toproduce G-3 fiberglass-reinforced epoxy or fiberglass-reinforcedphenolics of the kind used to produce G-10 and G-11fiberglass-reinforced phenolic are capable of performing at operationaltemperatures to which they would be exposed in physical vapor depositionprocesses and can be polished to provide the surface finish required.

A polymeric surface layer 804 may be applied using injection molding,extrusion, pultrusion, and casting/curing techniques. Polymeric surfacelayer 804 may be a precured film which is applied using an adhesivewhich is cured in a manner so that the cured adhesive will not outgasunder the process-operational conditions at which insulating sealingstructure 133 must perform.

When the insulating surface layer 804 is comprised of an inorganicmaterial such as aluminum nitride, silicon nitride, or silicon oxide, apreferred method of application of surface layer 804 over rigid centralportion 802 is by physical vapor deposition, preferably by sputtering.Sputtering of aluminum nitride, silicon nitride, or silicon oxide can beaccomplished using standard sputtering techniques and a target comprisedof the desired compound. The target may also be aluminum or silicon,with the compound being formed by the addition of nitrogen or oxygen asa reactive gas during the sputtering process. Reactive sputteringtechniques are well known in the art.

When insulating surface layer 804 is comprised of one of the inorganicmaterials listed above, a preferred material for rigid central portion802 is aluminum, and more preferably aluminum having a layer of aluminumoxide on its surface.

FIG. 8B shows a preferred embodiment in which the main insulator sealingstructure 133 has a rigid central portion 812 comprised of aluminum. Thesurface of the aluminum has been anodized to produce aluminum oxidelayer 814, and finally, a finishing insulating layer of silicon nitride816 has been applied over the surface of aluminum oxide layer 814.

Aluminum oxide layer 814 serves three purposes: It provides a portion ofthe required dielectric strength; it provides a continuous coatingunderlying finishing insulating layer 816, to compensate for anypinholes in finishing insulating layer 816; and, it provides a goodbonding surface for attachment of finishing insulating layer 816.

The surface 818 of the silicon nitride layer 816 has been lapp polishedto a surface finish having a roughness height of less than about 0.40 μmin the direction perpendicular to the seal to enable sealing against amating surface against a vacuum of at least 10⁻⁶ Torr. Preferably, thesurface 818 is polished to a roughness height of less than about 0.20 μmto enable a seal against a vacuum of between about 10⁻⁸ and 10⁻⁹ Torr.Although the finishing insulating layer for this particular embodimentis silicon nitride, aluminum nitride and silicon oxide would be expectedto perform as well.

Finishing insulating layer 816, in combination with aluminum oxide layer814 provides the required dielectric capability necessary to preventvoltage breakdown under the operating conditions previously specified.Silicon nitride exhibits a volume resistivity of about 10¹⁵ Ω-cm, andhas a dielectric strength of about 3.6 to 9.6 V/mil, depending onthickness and method of fabrication. The thickness required for thesilicon nitride finishing insulating layer 816 is at least about 20-25Å, presuming no electrical insulation contribution from the aluminumoxide layer.

The preferred embodiments of the present invention, as described aboveand shown in the Figures are not intended to limit the scope of theinvention, as demonstrated by the claims which follow, since one skilledin the art can, with minimal experimentation, extend the scope of theembodiments to match that of the claims.

What is claimed is:
 1. An electrically insulating sealing apparatususeful in semiconductor processing when sealing against a vacuum of atleast 10⁻⁶ Torr, comprising a three dimensional structure having atleast three exterior surfaces, wherein said structure has a volumeresistivity of at least 10¹² Ω-m; a deflection temperature at 264 PSI(1.82 MPa) of at least 300° F. (148.9° C.); and a surface finish on atleast two of said exterior surfaces of 16 μin. (0.40 μm) or better inthe direction perpendicular to the seal.
 2. The electrically insulatingsealing apparatus of claim 1, wherein at least a portion of said threedimensional structure is plastic and wherein a water absorption of saidplastic is less than about 2.5 %.
 3. The electrically insulating sealingapparatus of claim 1, wherein the linear coefficient of expansion ofsaid plastic is less than 50×10⁻⁶ in./in./° F. (90×10⁻⁶ mm/mm/°C.) attemperatures below about 300° F. (148.9° C.).
 4. The electricallyinsulating sealing apparatus of claim 2, wherein the notched izod impactstrength of said plastic is at least 1.0 ft-lbs/in (52 J/m).
 5. Theelectrically insulating sealing apparatus of claim 2, wherein theultimate compressive strength of said plastic is at least 15,000 PSI(103.4 MPa).
 6. The electrically insulating sealing apparatus of claim2, wherein said plastic is selected from the group consisting ofphenolic, epoxy, polyetherimide, polyimide, and polyetheretherketone. 7.The electrically insulating sealing apparatus of claim 6, wherein saidplastic is a fiberglass-reinforced epoxy or a fiberglass-reinforcedphenolic.
 8. The electrically insulating sealing apparatus of claim 1 orclaim 2, wherein said three dimensional structure is of single piececonstruction.
 9. The electrically insulating sealing apparatus of claim1 or claim 2 wherein said three dimensional structure is of multiplepiece construction, and wherein said multiple pieces are bonded to eachother.
 10. The electrically insulating sealing apparatus of claim 9,wherein an adhesive is used to accomplish said bonding.
 11. Theelectrically insulating sealing apparatus of claim 10, wherein saidadhesive is a glass-filled, epoxy-based adhesive.
 12. The electricallyinsulating sealing apparatus of claim 1, wherein at least one surface ofsaid three dimensional structure comprises a groove.
 13. Theelectrically insulating sealing apparatus of claim 1, wherein at leastone surface of said three dimensional structure comprises a continuouscontacting bead or molding.
 14. The electrically insulating sealingapparatus of claim 1 or claim 2, wherein at least one surface of saidthree dimensional structure comprises an elastomeric coating, whereby acontinuous seal is enabled between said at least one surface and anothersurface brought in contact with said elastomeric coating.
 15. A methodof providing an electrically insulating sealing surface between a firstchamber wall housing a cathode and a second chamber wall housing ananode of a sputtering apparatus, comprising: a) selecting a threedimensional structure having at least three exterior surfaces, whereinat least a portion of said structure is fabricated from a plastic havinga volume resistivity of at least 10¹² Ω-m; a deflection temperature at264 PSI (1.82 MPa) of at least 300° F. (148.9° C.); and b) placing saidthree dimensional structure between said first chamber wall housing acathode and said second chamber wall housing an anode in a manner suchthat a first continuous seal is created between a first surface of saidelectrically insulating sealing structure and said first chamber wall,and a second continuous seal is created between a second surface of saidelectrically insulating sealing structure and said second chamber wall.16. The method of claim 15, wherein said plastic provides the sealingsurface for at least said first or said second continuous seal. andwherein said sealing surface has a surface finish of 16 μin (0.40 μm) orbetter in the direction perpendicular to seal.
 17. The method of claim16, wherein said plastic has a surface finish of 8 μin. (0.20 μm) orbetter in the direction perpendicular to seal.
 18. The method of claim15, wherein at least one of said first continuous seal and said secondcontinuous seal is created by contact between a surface of saidelectrically insulating sealing apparatus and an O-ring.
 19. The methodof claim 18, wherein said O-ring is seated within a groove located uponsaid electrically insulating sealing apparatus.
 20. The method of claim15, wherein at least one of said first continuous seal and said secondcontinuous seal is created by contact between a continuous contactingbead of molding located upon at least one of said electricallyinsulating sealing surfaces.
 21. The method of claim 15, wherein atleast one of said first continuous seal and said second continuous sealis created by contact between an elastomeric coating present upon atleast one of said electrically insulating sealing surfaces.
 22. A methodof fabricating the electrically insulating sealing apparatus of claim 2,comprising: a) drying said plastic in pellet or powdered form, wherebypotential outgassing components are removed; and b) forming saidthree-dimensional structure using melt compression or injection molding.23. A method of fabricating the electrically insulating sealingapparatus of claim 9, comprising: a) selecting said multiple pieces tobe bonded to each other; and b) bonding said multiple pieces into asingle, three-dimensional structure.
 24. The method of claim 23, whereinsaid bonding is accomplished using an epoxy-based adhesive.
 25. Aninsulating sealing structure comprising: a) a rigid central portion ormember for inhibiting seal deformation; b) at least one electricalinsulator applied to said rigid central portion to provide at least twosealing surfaces, said electrical insulator having a dielectric strengthof at least 1.96 MV/min air; and c) said at least two sealing surfaceshaving a surface finish exhibiting a roughness height of less than about0.40 μm, to enable a seal against a vacuum of at least 10⁻⁶ Torr. 26.The insulating sealing structure of claim 25, wherein said seal is acontinuous seal.
 27. The insulating sealing structure of claim 26,wherein said enclosed area is at least 2304 in².
 28. The insulatingsealing structure of claim 25, wherein said rigid central portion ormember comprises a material selected from the group consisting of ametal, a fiber reinforced polymeric material, and a polymeric material,wherein said material does not outgas in a manner which prevents saidinsulating sealing structure from functioning properly under operationalconditions.
 29. The insulating sealing structure of claim 28, whereinsaid material is a metal.
 30. The insulating sealing structure of claim23, wherein said metal is aluminum.
 31. The insulating sealing structureof claim 30, wherein said aluminum has been treated to produce analuminum oxide surface layer.
 32. The insulating sealing structure ofclaim 25, wherein said material is a fiber reinforced polymeric materialand said fiber comprises a graphite, silicon nitride, silica, or glass.33. The insulating sealing structure of claim 25, wherein said materialis a polymeric material selected from the group consisting of phenolic,polyetherimide, polyimide, and polyetheretherketone.
 34. The insulatingsealing structure of claim 28, wherein said rigid central portion ormember comprises aluminum which has been treated to create a surfacelayer of aluminum oxide, and wherein said electrical insulator comprisesa polyimide.
 35. The insulating sealing structure of claim 28, whereinsaid rigid central portion or member comprises aluminum which has beentreated to create a surface layer of aluminum oxide, and wherein saidelectrical insulator is selected from the group consisting of siliconoxide, aluminum nitride, and silicon nitride, or a combination thereof.36. The insulating sealing structure of claim 35, wherein saidelectrical insulator was applied using a physical vapor depositiontechnique.
 37. The insulating sealing structure of claim 28, whereinsaid electrical insulator is selected from the group consisting ofphenolic, polyetherimide, polyimide, polyketone, polyetherketone,polyetheretherketone, epoxy, aluminum oxide, silicon oxide, aluminumnitride, silicon nitride, and combinations thereof.